Raman spectroscopy is an optical spectroscopy technique, which measures the inelastic scattering, i.e. Raman scattering of monochromatic light by a material to produce a spectrum characteristic of the material. Raman spectroscopy has been demonstrated to be a powerful non-invasive analytical technology for material characterization and identification.
Conventional Raman spectroscopy generally utilizes a well-focused laser beam to produce Raman scattering signal from the sample. This approach has the apparent advantage of relatively high efficiency in Raman signal excitation and collection. However, it also suffers from the following drawbacks. First, only a small volume of the sample is measured. Thus the collected Raman spectrum may not be very representative, especially for some non-uniform samples. Second, the tightly focused laser beam may cause damage to some delicate samples. Third, for diffusely scattering samples which are not transparent to the laser beam, this approach will only measure the Raman scattering signal from the surface layer of the sample. The majority of the material underneath the surface will be almost completely out of reach. There thus exists a need for an improved light delivery and collection device for performing Raman spectroscopy, which not only allows the measurement of a large area of the sample but also enables sub-surface Raman signal excitation and collection.